1. Field of the Invention
This invention relates to human-analogous type fingers and a hand mechanism which can be applied to various operations manually practiced by a human as an alternative mechanism, and more particularly, to human analogous type fingers and hands which can be utilized for end effectors of robots, artificial hands and various manipulators.
2. Description of the Related Art
Conventionally and practically used apparatuses of this kind include end effectors (hands) of an industrial robot, and the structures thereof are mostly such that two pieces of plates are opposed in parallel to each other and operated by a link mechanism and a linear guiding mechanism. When an object to be grasped is known, an end effector in a form suitable to the object is used. When several kinds of objects are to be grasped, exchangeable end effectors are used. The conventional end effector in which the opposed plates are operated by the link mechanism or the like is deficient in general applicability, flexibility and adaptability which are required for a robot. The exchangeable end effector has a structural limitation for enabling the exchange and another limitation that plural end effectors must be provided in the neighborhood of the robot for exchanging the end effector.
On the other hand, there are a five-finger-hand, a three-finger-hand and the like which are in the research and development stages. The main applicable field thereof is an artificial hand, and such hands aim at imitating human hands.
For example, one of such robot hands comprises three fingers arranged in a manner to allow each joint to be moved independently, as disclosed in Japanese Patent Laid-open Publication No. 279291/1990 and U.S. Pat. No. 5,062,673.
Another robot hand, disclosed in Japanese Patent Laid-open Publication No. 274989/1989, has such a structure that a pulley of each joint is independently driven by a wire rope passed through a hose.
An alternative hand is disclosed in Japanese Patent Laid-open Publication No. 124892/1987, in which each finger is composed of plural segments mutually jointed to each other, and each of the segments is engaged with a ball screw carried on an adjacent segment. The ball screw is drivingly coupled with a motor through a power transmission system comprising a worm gear, a pulley and a wire rope.
The examples disclosed in Japanese Patent Laid-open Publication No. 274989/1989 and U.S. Pat. No. 5,062,673 have some disadvantages in that: (1) a load applied to each wire rope is large and the elongation of the wire rope worsens the finger positioning accuracy and the accuracy of strength, and (2) a grasping force by the fingers is small, and the embodiment disclosed in Japanese Patent Laid-open Publication No. 274989/1989 has further disadvantages in that: (3) since the hoses cannot be bent in a small radius of curvature, it is not suitable for a working robot and the wire hoses will cause interference during operation, and (4) frictions between the hoses and the wire ropes are large.
Another example disclosed in Japanese Patent Laid-open Publication No. 124892/1987 has also some disadvantages in that: (1) the structure of a power transmission system is complicated and the power loss is large, (2) since the fingers do not bend even though an external force is applied to the tips of the fingers, such fingers are not applicable in case of grasping fragile objects, and (3) since the correlation between a first finger and a second finger is fixed, the object which can be grasped is limited.